An image forming apparatus employing an electrophotographic system, such as a copying machine, printer, and facsimile machine, generally forms an electrostatic latent image in a method as described below. Namely, a corona charger, etc., provided on a photosensitive body uniformly charges an entire surface of the photosensitive body, and then a laser exposing device, etc., irradiates light on the photosensitive body in accordance with image data.
In a conventional image forming apparatus as described above, members for a charging step and members for an exposing step need to be separately located in the vicinity of the photosensitive body. Thus, it is difficult to miniaturize the apparatus. For this reason, techniques for unifying the charging step and the exposing step have been suggested. There is an ion flow recording technique known in the art. In this technique, ion flow generated by corona discharge is controlled on a pixel basis by control electrodes; and an electrostatic latent image is written directly onto a latent image carrying body.
However, the corona discharge utilizes an avalanche phenomenon under a high electric field, and is used in a so-called discharge flow area. Therefore the corona discharge generates ozone as a product of the discharge. Since it is not possible to continuously obtaining a discharge current (Id) stably if a wire electrode is used for the discharge, for example, the discharge current (Id) is generally stabilized in such a manner that a shield case is provided in the vicinity of the wire electrode, and a large current (Ic) is applied to the case. In such a system, the ozone is generated in large quantities. In other words, the system using the corona discharge phenomenon as described above can miniaturize the device, but cannot clear the problem of environmental pollution due to ozone. Consequently, it is difficult to put this system into practice.
In view of the foregoing problems, the present invention has an objective to provide a charging device which does not cause a problem of environmental pollution due to ozone.